Preparation and use of iron as a precipitant



Feb. 9, 1937. H E. KEYES 2,070,134

PREPARATION AND USE OF IRON AS A PRECIPITANT Filed Oct. 6, `1934 GMM/MAF Patented Feb. 9, 1937 anions;

PATENT, OFFICE PREPARATION AND USE OF IRON `AS A PRECIPITANT Harmon E; Keyes, Miami, Ariz; Application october s, 1934, serial No. 147,256

1o claims. A(c1. '151o9 In certain metallurgical processes the use of metallic iron to precipitate another metal, such as copper, in elemental form has long been practiced. The method here described relates particularly, but is not necessarily confined, to the precipitation of cement copper by metallic iron, either from clear solution or in the pulp. In case of precipitation of copper in the pulpmechanical agitator tanks or rotating devices such as mills or drums have foundv use in practice.

Either of the above types of precipitating de- Qvicesmay be applicable in the method here described. For example, the iron may be so finely divided as to permit of agitation in a stationaryI tank with a mechanical agitator, or it may be of y any desired size and precipitation accomplished by rotation in a properly designed mill.'

By my method -iron is produced' suitable forA either type of Vprecipitator and also improved results are accomplished in recovering cement copper by otation because of the novel characteristics of the cement copper wheriprecipitated by the form ofviron produced, and under the conditions given, in my method here described.

In case of Iprecipitating copper back into the pulp, such as originally described by Terry, 1,589,615, the ore containing oxidized copper is generally leached with sulphuric acid and agitated .with metallic iron as in a`mill or drum.

According to later improvements treatment is givenY to inhibit 1re-solution of cement copper and to increase the loatability by regulation of the hydrogen ion concentration of the pulp solution as described in my Patent No. 1,971,416, and theA copper is then recovered from the pulp by otation. The method here described relates chiefly to improved means of producing a more suitable .45 former practice the securing of iron in a suitable physical and chemical form and also the tendency 'of cement copper to re-dis'solve/v due to aeration after precipitation have been major problems. However, in my method tlf/ie iron to easily produced in a vform physically adaptable to use either in an agitator tank or drum and also chemically reactive to the copper solution, the resulting cement copper is readily amenable to recovery by otation and .the tendency to 55 re-solution is much lessthan with cement copperl produced by forms of iron previously employed, as will behereinafter more fully described. In former practice either sponge iron or scrap has been' used as a precipitant. Former attempts to subdivide moltenl iron by a jet of air or 'water or other means have failed to produce material suitable for precipitation due to inert coatings of magnetite formed on the particles during cooling. Sponge iron oiers difllculties in tech- Anique of production and scrap iron presents lo problems in manipulation.

Even when line scrap, such as cut up tin or de-tinned scrap is employed a locked mass of jagged and irregular particles is formed in the precipitating mill which, in spite of the large surface exposed, en- 15 trains particles of cement copper within 'the mass and because of the shortcircuited copper-- iron couple in copper solution-thus formed, galvanic action causes growths of metallic copper nodules up to one-half inch or more in size which oier considerableannoyance and require special means or frequent'shutting/ down and cleaning out o'f the entire chargein the precipitating mill for'their elimination.v In contradistinction tothe above, my method offers the following distinctive and novel improvementsl y l. The ironv precipitant is cheaply and easily produced as rounded grains, prills or pellets by a special method of preparation involving so breaking up a stream of molten iron bythe aid of water or steam,v ordinary forms of cheap iron such as eld scrap, pig iron or molten iron from any source being used. g

2. By the use .of theser small spheres or vpellets, whichI may vary -in size -from minus 100 ,mesh up to the minimum size which could be Aconveniently cast individually, a high degree of mobility of the metallic iron particles in the charge is secured during the rotation of the preo cipitating mill. Thus, by reason of its freedom` of action in moving about through the charge and its motion relative to the charge, a single particle of iron makes more eiiicient contact with the solution than does an equal iron surface but in other physical fo s, so that small spheroid particles yprecipita e copper in a highly ,efficient anda novel manner. e

3. Because of the high degree of mobility of the pellets of metallic iron in the charge and the absence of locked particles vof flat metallic iron, metallic copper particles are not entrained in the f charge but are freely discharged with the pulp, thus tending to prevent growth of copper granules which segregate in the drum.

4. By the use ofA small rounded iron pellets .there is sulcient grinding action afforded during precipitation to grind up any large particles' per is much more resistant to re-solution than ordinary ilocculent .cement copper as produced by the usual forms of scrap iron. This crystalline form of copper is made possible by use of iron produced according to my method.

7. The type of iron here employed is easy and cheap to handle, transport and feed mechanically, -due to the rounded shape and small size of the individual particles.

'8. The iron here employed is free from foreign matter such as rubbish and copper and brass scrap as is found in commercial reclaimed scrap iron or tin scrap.

9. Iron produced by this method is much'more brittle than ordinary cast iron and Amay therefore be ground in .the precipitating mill to a greater extent than ordinary iron, by employing means for impact; yhence a relatively large amount of very nely divided iron may be thus 'produced which increases the precipitating ac tion in the mill.

10. The iron pellets produced and used in this method are porous and in some cases denitelyv hollow, thus giving increased precipitating surface as compared to the usual solid form of iron' of the same general shape and weight.

11. The iron pellets or grains producedby this method are-free from the usual coating of mag' netite which forms when molten iron cools in an oxidizing atmosphere. By employing my methodtheiron surfaces produced on the subdivided particles are clean, bright and chemically reactive to the copper sulphate solution. However, if the particles are exposed to air during cooling the surfaces are inert in the copper sulphate solution until the magnetite coating may be Worn oil?. i

12. The cement copper produced by this method being more dense and crystalline than the usual forms, the product resulting from treatment withthe iron pellets settles much more rapidly than ordinary cement copper, hence the thickening and filtration steps in cement copper clean-up are greatly improved, cheapened and simplied. 13. Because of the rapid precipitating action of these small pellets and the possibility of crushing the pellets by impact in a mill, thus giving even greater precipitating action, this form of iron may be advantageously employed as an adjunct to precipitation using a ball mill and con-l ducting grinding, leaching and multaneously in the mill.`

14. By employing suitable vimpact in a vmill the precipitating si- `iron grains or pellets produced by this method may be ground to any desired fineness, because of their brittleness, and used for various industrial purposes.

.As distinguished from former practice my method employs asa principle of operation the subjecting of a falling stream of molten iron to -to use the device illustrated in Fig. 1.

the effect of impact accompanied by an atmosphere of steam or immersion in water so as to eect sub-division of the molten iron into small particles `or pellets together with rapid coolingout of contact with air, thereby producing small particles of iron free from the usual coating of magnetite scale. By quenching in water from the molten state the pellets are porous or sometimes hollow and furthermore a. form of cast iron different -from the usual types with respect to the state of combination of iron and carbon is produced. This treatment results in a very high percentage ofcombined carbon, giving a modied type of white iron which, due to its peculiar micro-structure of iron and carbon is not only extremely brittle and comparatively easy to crush by impact, but causes copper to be deposited from solution on its surface in a bright, dense and crystalline form as compared to the usual occulent, loose and spongy cement copper resulting from the various forms of commercial iron formerly used. Furthermore, I have found this crystalline Vform of copper much more plate for breaking up the stream of molten iron;

Figure 3 is a. device also adapted to produce finely divided particles, 'but employing the use of a jet ofsteam in lieu of the splash plate.

If it is desired to produce relatively coarse particles, (for instance, from 1A to I/fy) I prefer vice consists of a tank designatedgenerally l, which is adapted to hold a body of water 2, or

some other non-oxidizing liquid. Extending upwardly from the body cf liquid 2 is a pipe 3 which is closed at its upper end as at 4 by a block which is preferably composed -of refractory material.

'I'he upper side of the 'block 4 is cut out to form a cup 5. Molten metal 6 is poured into the cup from a spout 1, or some other feeding means. A channel 8 is drilled from the cup through the block il.

This dewater 2, the metal'vis further subdivided and forms in rounded pellets, as indicated by the numeral l2. The body of Water 2 is of suilicient depth so that the iron is solidified While falling and no agglomeration the container. v

A suitable drag or screw conveyor may be provided toremove the pellets from the base of the container I, and I have-shown in Fig. 1 a'drag conveyor I3, which carries the pellets over a drying hearth. I4 after they are removed from the water, and then discharges the dried pellets into a bin l5. I find vthat the iron formed in the ap' paratus of Fig. 1, is'particularly adapted-foruse in a drum or mill precipitator. The pellets so formed are mainly 1/8"to 1/2" in diameter, therelby'offering a suiciently large surface for eiective precipitation, but at the same time small takes place in the base of fil i 2,070,1s4 enough to be fed mechanically and to be carried along in the pulp stream into the drum.

lWhen the molten iron is poured-directly into a body of water, as in Fig. 1, I have found that the pellets formed thereby are quite porous and insom'e cases consistof hollow spheroids. This, of course, creates increased surface areas exposed to the copper solution, as opposed to solid particles of thev same size and weight.

I have also found that cast iron chilled in water from the molten state precipitates a dense, coherent copper, rather than the usual ilocculent, spongy and finely divided form encountered in practice. This coherent product is readily dislodged as thin flakes by mild abrasion so that in a precipitating mill clean iron surfaces are constantly exposed. This, of course. maintains a high precipitating efiiciency and the cement copper thus produced is flaky rather than powdery and less susceptible to oxidation and re-solution than 'the usual form. Moreover, the extremely brittle nature of this type of iron makes possible' its crushing and grinding by impact in the mill to a much greater extent than is the case with iron formerly used. Thus, the precipitating capacity of the mill maybe enhanced vby this increased production of finely divided iron duringV rotation. Therefore, processes which conduct grinding of the ore, leaching and precipitation simultaneously in a ball mill may use to advantage the form of iron produced by my method to `increase the precipitating action vin the mill.

In addition tothe vphysical characteristics of iron produced according to my invention, I have found that the sudden chilling caused by pouringmolte'n iron into,` water results in a type of iron-carbon combination not only/more brittle than the usual forms of cast iron but other characteristicsimportant for the copper precipitation step have been discovered.

In Figure 2, it, will be observed that the stream of molten metal 9 is broken up by impacting upon a splash plate I6 which slopes downwardly from the pipe `3. It will be noted that the pipe 3 in Fig. 2 is somewhat larger-than the pipe of Figure l, although when using a splash plate the metal need not fall as great a distance as when it is poured directly into the water. AI also prefer that a stream of water l1 be directed over the splash plate from a'nozzle I8 or other suitable 'cured by the use of the splash plate. Furthermore, the stream of water I1 furnishes va shear- `ing action by the metal impinging on the splash plate, thus contributing to the sub-division of the metal, as well as sluicing the iron particles into the body of water below.

The exact conditions as to height of drop ofthe iron stream, inclination of the splash plate, size of opening for pouring the iron, amount of water added to plate and mannenof collecting the iron are matters to be acusted to suit specific requirements. By concentrating the stream of water at the point where the iron strikes the plate not only is the iron stream broken up into very fine particles but the plate is cooled at the point of impact with the iron and building up of iron on the plate prevented.- Sticking of the molten iron on the plate is further prevented by use of asuitable refractory material. After the finely subdivided iron is cooled it is removed from the waconveyor, and is then rapidly dried to preven oxidation. If part of this product is too coarse for treatment in the agitator type of precipita.- tor such oversize is eliminated as by screening before use. The oversize is suitably used in the drum or mill type precipitator. i In Figure I have shown a method of accompllshing subdivision of the stream 9 of molten metal by the use of a jet of steam I9 which is directed on the stream 9 by anozzle 20. The use of the steam jet usually result in a relatively fine sub-division of the metal, but proper control of the jet will vary the size of the iron as desired. It will be appreciated that under certain conditions, some other inert-gas may be employed in lieu of steam. i The conditions relative to the rate of water and iron addition may be so regulated as to produce a temperature within the pipe 3 which is -sufllcient to produce an atmosphere of steam therein, thus preventing oxidation of the iron particles. If desired, however, additional steam may be introduced as at 2l in Fig. l, and may discharge through the outlet 22. While I have shown the use 4of steam in Fig. l only, it is, of

l corse, apparent that" it may be used in such apparatus as shown in Figs. `2 and 3,'when desired.

Also, it will be appreciated that a suitable drag `conveyor and drying arrangement may be employed in Figs. 2 and 3.-

From the foregoing it will be noted. that the fundamental feature of my invention is the sub-- division of molten iron into smallparticles or pellets under reducing or inert conditions so that the usual magnetite coatings on the iron `sur- 2 will depend largely `In treating cement copper as produced byformer f standard types of iron the Yre-solution problem is one of large proportions unless inhibited by means such as adding alkaline precipitant as described in my Patent No. 1,971,416. However, I have found that the cement copper produced by iron prepared as in this'vmethod has different characteristics and is not dissolved by the aeration treatment to nearly the extent as is the case with cement copper produced from forms of iron previously used.

The conducting of this method'and'the novel results accomplished will be more clearly illustrated by the following examples.

(1) Iron was poured through 1% hole through an empty 50 gal. steel drum shell set on top of a similar drum half full of water. An inclined splash plate was set over the water and the stream of water directed onto the plate at point of iron impact. The iron was broken up into fine particles and washed into the body of water below. Particles that were washed directly into the water showed clean bright metallic iron surface. When conditions were properly regulated, the molten iron was broken up into minute spheres.

`(2) Conducted similar to (1), but removed splash plate and filled lower drum .with water. pouring iron directly into water. The iron did not y into the air on striking the watenbut this result and the and the Y i broke up as pellets having the following screen analysis:-

' Per cent |l inch None -i-.525 inch 6.44 -|-.263 inch 44.45 -i- 10 mesh.. 46.70

+28 mesh s; l i 1.99

, 48 mesh 0.29 +100 mesh L 0.08 100 mesh l 0.05

lar cast iron ball pared to 260 lbs. for solid regular cast iron balls worn down to the same diameter as thefpellets.

These cast iron `balls could not be broken with a hand hammer on a steel plate as was done with the pellets, indicating the latter to be much more brittle than ordinary cast iron.

(3a) Precipitation tests were made, using cut up tin can scrap, steel turnings, cast iron turnings and the quenched pelletslprepared by my method. Similar amounts of neutral copper sulphate solution were added to each type of iron 'in a separate beaker. After standing about an hour it was found that all samples except the quenched pellets had a loose and spongy type of cement copper deposit which readily became dislodged and broke into a e sludge. However, the chilled pellets produced a lighter colored deposit of bright copper with a metallic luster whichV became dislodged by mild abrasion and formed thin scales or akes resembling metallic Lcopper ground into akes.

(3b) The above test was repeated, using small cast iron balls in comparison' with the. chilled pellets. The copper which deposited on the reguy was also spongy, occulent and loose as before, while the deposit ou the chilled pellets was more crystalline, coherent, dense and bright.

(4) Complete laboratory tests were made illustrating leaching, precipitation and cement copper flotation, using the chilled iron shot pellets to precipitate the copper' in the leached pulp and employing a laboratory size wooden drum as the precipitator. The samples of leached pulps were cut from thetnal leaching agitator in a commercial scale operation.

(a) The first preliminary test employed a 21/2 liter bottle hand shaking for precipitation. Using an ore `charge of about 1200 grams at 45 percent solids, together with 2082 grams of iron, minus 0,-525" andplus 10 mesh, andy'by hand shaking the copper .precipitation was complete Ain 15 minutes, as shown by sodium sulphide test.

Fl'lotation was conducted with 0.125 lb. o`f a rela.- tively insoluble organic sulphur derivative compound and 0.10 lb. pine oil per ton ore. `'I'he assays and copper distribution were as follows:

Cgffg" Middiing 'raiung Assay percent copper k36.19 1. 52 j 0.085 Distribution, percent sau 5.06 11.20

"my method, thus` solving one ofI the The head value was calculated at 0.73 per cent copper. l

(b) Further similar tests were run using 7100 grams of the chilled iron pellets and shot in a laboratory rotary drum, the samples representing approximately 2 100 grams of solids and the percent solids being 40-45. Precipitation of copper was complete in 15 .minutes and was followed by flotation with 0.0 7 lb. of the said relatively insoluble organic sulphur derivative compound and 0.06 lb. pine oil per ton o re. The rougher concentrate was re-iloated in a cleaner, thus giving a nal concentrate, cleaner reject and tailing as products. Tests were run without and with addition of lime between copper precipitation and flotation, the function of the lime being to inhibit resolution of cement copper. The following results Were obtained without using lime:

Cleaner Tailing Percent Heads q l Concn. Reject tion Solids Copper assay 1.51 60. 7. 37 0. 060* 0. 14 Copper distribution. 100.00 64.00 27.09 0.29 8.62

*Assay in pounds copper per ton solution.

Addition of suicient lime prior to flotation and .Y

after iron treatment so as to precipitate 5-10 percent 'of the dissolved iron gave the following results:

*Assay in pounds copper per ton solution. The last two tests show a satisfactory grade of concentrate and all three tests gave a satisfactory tailing.' More effective flotation could .be secured by using additional otation reagent. These tests show that both a high grade concentrate and a low tailing may be simultaneously produced by using the iron pellets as above described. Furthermore it was noted that the copper thus produced occurred largely as very fine ilakes which retained their mitallic luster and settled much more rapidly than the powdery cement copper produced'by ordinary iron. It is a noteworthy fact that the ordinary cement copper as usually produced in standard flotation tests with' tin scrap as a precipitant shows by laboratory test about 3.0 per cent of the precipitated copper re-dissolved during flotation without use of lime and 1.4 per cent similarly redissolved if lime is used as aforesaid. By comparing these re-solution figures with the above tests using the chilled iron pellets Vit is seen that this re-solution is cut to about one tenth of its normal value by using iron prepared according to main obstacles in cement copper flotation.

In summary, this' method not only furnishes an economical iron supply from adequate so1 rces, but produces iron in a more suitable form, the precipitation treatment resulting in a new type of cement coppei` for flotation which is more readily settledand filtered and has va much less tendency to re-dissolve during' the treatment process, as compared to cement copper produced from the usual types of metallic iron formerly employed. Furthermore, the thin, minute ilakes of copper produced by this method gives 'it advantages for use as a base for copper paints and pigments. The iineness of the cement copper :Hakes is governed somewhat by the abrasive action in the mill, which in turn is controlled by tlie peripheral speed and the lifters installed in the mill. i

As pointed out abovemy inventionis applicable either when the copper is precipitated from a pulp or from clear solution, and the appended claims are to be considered as covering both types of process. Furthermore, the term abrasive as used in the appended claims is to be construed as covering attrition or impact as well as lstrict abrasion.

While I have shown and described the preferred embodiment of my invention, I wish it to be understood that I do not conne myself to the precise details herein set forth by way-y of illustration, as it is apparent that many changes and variations may be made therein, by those skilled in the art, Without departing from the spirit of the invention, or exceeding the scope of the appended claims.

I claim:

l. In a process for precipitating copper by contacting the copper solution with metallic iron,

the step of preparing the precipitant by pouring' molten iron in a small stream, breaking up said molten iron stream into rounded particles, introducing said particles into a bath to solidify them,- adding said particles to the copper solution, and

the steps of preparing the precipitant by pouring I molten iron in a small stream, breaking up said molten iron stream into rounded particles by the action of a. jet of inert gas, solidifying the said particles out of .contact with air, andthen adding the iron particles so produced to the copper bear-V ing solution.

4. In a process for precipitating copper by conta'cting the copper solution with metallic iron,`

the step of preparing the precipitant by pouring molten iron in a small stream into a non-oxidizing atmosphere, breaking up said molten iron stream into rounded particles, solidifying said particles out of contact with air, and adding said particles to the copper solution.

5. In a method of precipitating copper by iron, the step of preparing the precipitant by pouring molten iron onto a solid surface to sub-divide theA iron into a plurality of particles while at the same timedirecting a sheet of water across said surface, cooling said sub-divided iron particles under non-oxidizing conditions and then adding said iron particles to a copper bearing solution.

6. In a process for precipitating copper by contacting a leached pulp with metallic iron, the steps of preparing the precipitant by pouring molten iron into a bath of non-oxidizing liquid,

adding said particles to the copper solution, and

dislodging the precipitated copper adhering to said'particlesv by subjecting the particles to an abrasive' action.

8. In a process for recovering copper by contacting a leached pulp with metallic iron and vthen subjecting the pulp to flotation, the steps of preparing the precipitant by pouring molten iron into a bath of non-oxidizing liquid, cooling said iron in the liquid, adding the iron to the copper solution in a rotary mill which is provided with a grinding medium, and passing the effluent pulp from the mill to a otation stage.

9. In a process for precipitating copper by contacting dissolved copper with metallic iron, the step vof preparing the precipitant by pouring vmolten' iron in a small stream, breaking up such iron stream into rounded particles, and introducing said particles into a bath of non-oxidizing liquid to solidify them.

10.In a process for precipitating copper by contacting dissolved copper with metallic iron, the step of preparing the precipitant by pouring molten iron into a bath of non-oxidizing liquid, cooling the iron in said bath, adding said iron to a copper solution, and then crushing the iron in the presence ofthe solution.

HARMON E. KEYES.

Patent No. 2,070,134 Granted February 9, 1937 HARMON E. KEYES The above entitled patent was extended October 2, 19517 under the provisions of the Act of June 30, 1950, for 6 years and 83 days from the expiration of the original term thereof.

Ummnssz'oner of Patents. 

